Non-pneumatic tire

ABSTRACT

A composite material comprises a plurality of springs forming a structure embedded within a polymer. Each spring is interwoven with at least one other spring thereby forming an entirely polymer-coated structure.

FIELD OF THE INVENTION

This invention relates to a composite material and, more specifically,to a composite material exhibiting unique and unexpected physicalcharacteristics.

BACKGROUND OF THE INVENTION

Conventional non-pneumatic solid rubber tires have been used prior topneumatic tires. As vehicle speeds increased and ride characteristicsbecame more important, the need for a pneumatic structure emerged. Thepneumatic tire provided a solution to the problems and limitations ofsolid, non-pneumatic tires.

The conventional pneumatic tire is an efficient structure that hasendured as a solution to conventional vehicle requirements. Theconventional pneumatic tire is a “tensile structure.” Tensile structurescontain a compression structure for providing a tensile preload in thetensile structure. The tensile structure may typically accept nocompression, and the compression structure, no tension. In pneumatictires, cords are the tensile structure and compressed air is thecompression structure.

A drawback of a conventional pneumatic tire is that it is pneumatic. Aircontained under pressure may, and typically does, escape at inopportunetimes, at least from a vehicle operator's view point.

A non-pneumatic tire has no air under pressure. It is a tire structurethat performs similarly to a pneumatic tire, without requiring aircontained under pressure. Communication of a non-pneumatic tire with aroad/contact surface in the area of the tire footprint, or contactpatch, provides the only force input to the vehicle from the contactsurface and provides the handling forces and load to the contactsurface. Thus, a non-pneumatic tire has these fundamentalcharacteristics in common with a pneumatic tire.

A conventional pneumatic tire has unique flexure and load carryingcharacteristics. Shock and deflections, although occurring locally inthe area radially inwardly of the footprint, may be absorbed globally bythe entire tire structure. Cornering characteristics are achieved by acombination of increases and decreases in tension of the tire sidewall.

A conventional non-pneumatic tire must similarly be able to withstandshock loads and dissipate absorbed energy. However, unlike a pneumatictire, a non-pneumatic tire typically absorbs shocks and deflects locallywithin the footprint or contact patch. Such localized deflection of anon-pneumatic tire must therefore also exhibit high dampeningcharacteristics.

Further, any tire in a running condition must be able to dissipate heat.The nature of dampening loads is a form of energy dissipation. Energyabsorbed is converted to heat. Heat, in turn, may affect tireperformance and may result in premature tire failure. Thus, efficientdissipation of heat is essential for any tire. Ideally, energy is onlyabsorbed by the tire in the area radially inward of the footprint orcontact patch so that energy may be removed from such area during theremainder of the tire's revolution.

However, rubber is a poor conductor of heat. The thicker the rubber, thegreater the heat accumulation. The heat accumulation may be mitigated toa controlled level by having thin material cross sections with high aircirculation.

Urethane tires can operate at temperatures as high as about 93° C. (200°F.). Temperatures higher than 121° C. (250° F.) degrees for prolongedperiods will cause a weakening of the urethane. If the temperature of aurethane tire rises high enough, premature failure of the urethane tiremay occur.

One conventional non-pneumatic tire/wheel includes a central portion ofresilient material, an outer resilient tread portion, and an interposedshock absorbing portion comprising a plurality of crossed webs ofresilient material formed with the center and tread portions. Formed inthe inner portion of the shock absorbing portion is an annular series oforifices. The orifices are set transversely and slightly overlapping.Each orifice extends across the entire axial width of the shockabsorbing portion. A pair of disks is also provided with similarorifices. One disk is positioned on each side of the tire/wheel withorifices aligned with those of the shock absorbing portion. Uponmolding, one integral unit is formed. This cushion tire/wheel eliminatedthe metal parts used to fasten a pneumatic or solid rubber tire to awheel.

Such conventional attempts to develop a non-pneumatic tire failed toprovide adequate heat dissipation along with adequate load bearingcapability. As vehicle speeds have increased, these concepts have beenincapable of meeting the needs of the passenger and truck tires.

Another conventional non-pneumatic tire is integrally molded from anelastomeric material to form a unitary structure comprising inner andouter “hoops.” The outer hoop is supported and cushioned by a pluralityof circumferentially spaced apart planar ribs and a planar central web,which connects the hoops at their circumferential center. The web liesin a plane perpendicular to the rotational axis of the tire. The ribsextend axially along the inner and outer hoops connecting the hoops withedges of the ribs along opposite faces of the web. The planar ribs maybe undercut at the radial extremes to assure bending and no bucklingunless a critical load is exceeded.

Another conventional non-pneumatic tire has an equatorial plane, an axisperpendicular to the equatorial plane, an annular tread rotatable aboutthe axis, and an annular elastomer body made from a material having aShore A hardness in the range of 60 to 100. The elastomer body has firstand second spaced lateral sides. The sides are spaced equidistant fromthe equatorial plane and extend between the tread and the rim. The bodyhas openings positioned equidistant from the axis, some of which extendfrom the first side and others which extend from the second side to formfirst and second sets of openings. The sets of openings extend fromrespective sides toward the equatorial plane. The openings form equallyspaced columns of elastomer material in the body. The columns formed bythe first set of openings are inclined to the radial direction of thetire, and the columns formed by the second set of openings are generallyinclined to the radial direction of the tire, but are opposite ininclination with respect to the columns formed by the first set ofopenings.

The National Aeronautics and Space Administration (NASA) has developedsurface vehicles to support long range lunar exploration and thedevelopment of a lunar outpost. These vehicles are heavier and travelgreater distances than the Lunar Roving Vehicle (LRV) developed for theApollo program in the late 1960s. Consequently, new tires will berequired to support up to ten times the weight, and last for up to onehundred times the travel distance, as compared to those used on theApollo LRV, thereby requiring operational characteristics similar topassenger vehicles used on earth. However, conventional rubber pneumatictires cannot function acceptably in space.

For example, rubber properties vary significantly between the coldtemperatures experienced in shadow (down to 40 K) and the hottemperatures in sunlight (up to 400 K). Further, rubber degrades whenexposed to direct solar radiation, without atmospheric protection.Finally, an air-filled tire is not permissible for manned lunar vehiclesbecause of the possibility of a flat tire. To overcome theselimitations, a tire design has been developed for the Apollo LRV and wassuccessfully used on Apollo missions 15, 16, and 17. This non-pneumatictire was woven from music wire, which was robust to lunar temperaturevariations and solar radiation, operated in vacuum, and did not requireair for load support. This structure further functioned to contour tothe lunar terrain, which facilitated traction and reduced vibrationtransfer to the Apollo LRV.

As stated above, because of the new weight and distance requirements forlunar vehicles, a tire with greater strength and durability wasrequired. One conventional wheel and non-pneumatic tire assembly has avariable diameter which, in addition to changing its diameter, may alsochange its width, thereby increasing the area of the wheel that engagesthe ground. Thus, this non-pneumatic tire may be adjusted to increase avehicle's performance according to the terrain over which it istraveling. This tire/wheel has arching members with first and secondends connecting a wheel hub. The arching members extend outwardly in anarc between the first and second ends. The arching members form aplurality of flexible hoops spaced circumferentially around the hub andextending radially outward from the hub.

More specifically, this conventional non-pneumatic tire/wheel forms acage composed of thirty-eight equally spaced radially extending hoopsthat arch between axially outer rims of a hub. The hoops are made ofhelical steel springs filled by wires cut to a desired length andthreaded through the center of the springs. The conventional hub may beexpanded/contracted axially for varying the diameter of the tire/wheel.

The wire mesh design of the Apollo LRV tire was found to not be readilyscalable. Specifically, the increase in wire diameter to create a tirethat supported ten times the load of the original design created twosignificant limitations: 1) the ability to contour to the terrain waslost, thus limiting traction and ability to isolate vibration; and 2)the increased wire stresses limited functional life.

Thus, another conventional non-pneumatic tire/wheel includes a pluralityof helical springs. Each helical spring includes a first end portion, asecond end portion, and an arching middle portion interconnecting thefirst end portion and the second end portion. Each helical spring isinterwoven, or interlaced, with at least one other helical spring of theplurality thereby forming a woven toroidal structure extending about anentire circumference of the non-pneumatic tire/wheel. A subset ofhelical springs may be secured to a first annular rim of a wheel and/ora second annular rim of the wheel. A wheel with an annular rim at eachaxial side of the tire may secure the tire to the wheel. Thus, ascompared to structures of conventional pneumatic tires, the woven/lacedtoroidal structure of interwoven helical springs defines a first ply forthe non-pneumatic tire. A second ply may radially overlap the first ply.Such a second ply may comprise the same interwoven toroidal structure asthe first ply.

As a result, an improved composite material for a non-pneumatic tire isdesirable.

DEFINITIONS

“Apex” means an elastomeric filler located radially above the bead coreand between the plies and the turnup ply.

“Annular” means formed like a ring.

“Aspect ratio” means the ratio of its section height to its sectionwidth.

“Axial” and “axially” are used herein to refer to lines or directionsthat are parallel to the axis of rotation of the tire.

“Bead” means that part of the tire comprising an annular tensile memberwrapped by ply cords and shaped, with or without other reinforcementelements such as flippers, chippers, apexes, toe guards and chafers, tofit the design rim.

“Belt structure” means at least two annular layers or plies of parallelcords, woven or unwoven, underlying the tread, unanchored to the bead,and having cords inclined respect to the equatorial plane of the tire.The belt structure may also include plies of parallel cords inclined atrelatively low angles, acting as restricting layers.

“Bias tire” (cross ply) means a tire in which the reinforcing cords inthe carcass ply extend diagonally across the tire from bead to bead atabout a 25°-65° angle with respect to equatorial plane of the tire. Ifmultiple plies are present, the ply cords run at opposite angles inalternating layers.

“Breakers” means at least two annular layers or plies of parallelreinforcement cords having the same angle with reference to theequatorial plane of the tire as the parallel reinforcing cords incarcass plies. Breakers are usually associated with bias tires.

“Cable” means a cord formed by twisting together two or more pliedyarns.

“Carcass” means the tire structure apart from the belt structure, tread,undertread, and sidewall rubber over the plies, but including the beads.

“Casing” means the carcass, belt structure, beads, sidewalls and allother components of the tire excepting the tread and undertread, i.e.,the whole tire.\

“Chipper” refers to a narrow band of fabric or steel cords located inthe bead area whose function is to reinforce the bead area and stabilizethe radially inwardmost part of the sidewall.

“Circumferential” means lines or directions extending along theperimeter of the surface of the annular tire parallel to the EquatorialPlane (EP) and perpendicular to the axial direction; it can also referto the direction of the sets of adjacent circular curves whose radiidefine the axial curvature of the tread, as viewed in cross section.

“Cord” means one of the reinforcement strands of which the reinforcementstructures of the tire are comprised.

“Cord angle” means the acute angle, left or right in a plan view of thetire, formed by a cord with respect to the equatorial plane. The “cordangle” is measured in a cured but uninflated tire.

“Denier” means the weight in grams per 9000 meters (unit for expressinglinear density). Dtex means the weight in grams per 10,000 meters.

“Elastomer” means a resilient material capable of recovering size andshape after deformation.

“Equatorial plane (EP)” means the plane perpendicular to the tire's axisof rotation and passing through the center of its tread; or the planecontaining the circumferential centerline of the tread.

“Fabric” means a network of essentially unidirectionally extendingcords, which may be twisted, and which in turn are composed of aplurality of a multiplicity of filaments (which may also be twisted) ofa high modulus material.

“Fiber” is a unit of matter, either natural or man-made that forms thebasic element of filaments. Characterized by having a length at least100 times its diameter or width.

“Filament count” means the number of filaments that make up a yarn.Example: 1000 denier polyester has approximately 190 filaments.

“Flipper” refers to a reinforcing fabric around the bead wire forstrength and to tie the bead wire in the tire body.

“Footprint” means the contact patch or area of contact of the tire treadwith a flat surface at zero speed and under normal load.

“Gauge” refers generally to a measurement, and specifically to athickness measurement.

“Harshness” means the amount of disturbance transmitted by a tire whenit passes over minor, but continuous, road irregularities.

“High Tensile Steel (HT)” means a carbon steel with a tensile strengthof at least 3400 MPa@0.20 mm filament diameter.

“Hysteresis” means a retardation of the effect when forces acting upon abody are changed.

“Inner” means toward the inside of the tire and “outer” means toward itsexterior.

“Innerliner” means the layer or layers of elastomer or other materialthat form the inside surface of a tubeless tire and that contain theinflating fluid within the tire.

“LASE” means a load at a specified elongation.

“Lateral” means an axial direction.

“Lay length” means the distance at which a twisted filament or strandtravels to make a 360 degree rotation about another filament or strand.

“Mega Tensile Steel (MT)” means a carbon steel with a tensile strengthof at least 4500 MPa@0.20 mm filament diameter.

“Normal Load” means the specific design inflation pressure and loadassigned by the appropriate standards organization for the servicecondition for the tire.

“Normal Tensile Steel (NT)” means a carbon steel with a tensile strengthof at least 2800 MPa@0.20 mm filament diameter.

“Ply” means a cord-reinforced layer of rubber-coated radially deployedor otherwise parallel cords.

“Pneumatic tire” means a laminated mechanical device of generallytoroidal shape (usually an open-torus) having beads and a tread and madeof rubber, chemicals, fabric, steel, and/or other materials. Whenmounted on the wheel of a vehicle, the pneumatic tire, through itstread, provides traction and contains a fluid that sustains the vehicleload.

“Radial” and “radially” are used to mean directions radially toward oraway from the axis of rotation of the tire.

“Radial Ply Structure” means the one or more carcass plies or which atleast one ply has reinforcing cords oriented at an angle of between 65°and 90° with respect to the equatorial plane of the tire.

“Radial Ply Tire” means a belted or circumferentially-restrictedpneumatic tire in which at least one ply has cords which extend frombead to bead are laid at cord angles between 65° and 90° with respect tothe equatorial plane of the tire.

“Rim” means a support for a tire or a tire and tube assembly upon whichthe tire is secured.

“Section Height” means the radial distance from the nominal rim diameterto the outer diameter of the tire at its equatorial plane.

“Section Width” means the maximum linear distance parallel to the axisof the tire and between the exterior of its sidewalls when and after ithas been inflated at normal pressure for 24 hours, but unloaded,excluding elevations of the sidewalls due to labeling, decoration orprotective bands.

“Sidewall” means that portion of a tire between the tread and the bead.

“Spring rate” means the stiffness of a tire or spring expressed as theslope of a load defection curve.

“Super Tensile Steel (ST)” means a carbon steel with a tensile strengthof at least 3650 MPa@0.20 mm filament diameter.

“Tenacity” is stress expressed as force per unit linear density of theunstrained specimen (gm/tex or gm/denier). Used in textiles.

“Tensile” is stress expressed in forces/cross-sectional area. Strengthin psi=12,800 times specific gravity times tenacity in grams per denier.

“Toe guard” refers to the circumferentially deployed elastomericrim-contacting portion of the tire axially inward of each bead.

“Tread” means a molded rubber component which, when bonded to a tirecasing, includes that portion of the tire that comes into contact withthe road when the tire is normally inflated and under normal load.

“Tread width” means the arc length of the tread surface in a planeincluding the axis of rotation of the tire.

“Turnup end” means the portion of a carcass ply that turns upward (i.e.,radially outward) from the beads about which the ply is wrapped.

“Ultra Tensile Steel (UT)” means a carbon steel with a tensile strengthof at least 4000 MPa@0.20 mm filament diameter.

“Yarn” is a generic term for a continuous strand of textile fibers orfilaments. Yarn occurs in the following forms: 1) a number of fiberstwisted together; 2) a number of filaments laid together without twist;3) a number of filaments laid together with a degree of twist; 4) asingle filament with or without twist (monofilament); 5) a narrow stripof material with or without twist.

SUMMARY OF INVENTION

A composite material in accordance with the present invention comprisesa plurality of springs forming a structure embedded within a polymer.Each spring is interwoven with at least one other spring thereby formingan entirely polymer-coated structure.

According to another aspect of the present invention, each spring islaterally tensioned with an adjacent spring such that an inner part ofeach coil of each spring engages an inner part of each coil of theadjacent spring.

According to still another aspect of the present invention, each springis laterally compressed with an adjacent spring such that an outer partof each coil of each spring engages an inner part of each coil of theadjacent spring.

According to yet another aspect of the present invention, the springsare elliptical.

According to still another aspect of the present invention, the springsare constructed of a material from the following group: metal, plastic,polyurethane, rubber, and carbon.

According to yet another aspect of the present invention, the springsare constructed of Normal Tensile steel, have a 0.35″ spring outsidediameter, have a 0.055″ wire diameter, and a 0.28″ pitch.

According to still another aspect of the present invention, a bendingstiffness of the composite material is larger than a bending stiffnessof the springs and a bending stiffness of the polymer measuredseparately prior to forming the composite material.

According to yet another aspect of the present invention, the compositematerial forms a toroidal carcass structure extending about an entirecircumference of a non-pneumatic tire.

According to still another aspect of the present invention, the polymermay be, for example, Poly PT Flex 20, Poly PT Flex 60, Poly PT Flex 70,and/or Poly PT Flex 85 from Polytek Development Corporation of Easton,Pa. Another example material may be Repro Ultra Light Fast-Cast Urethanefrom Freeman Manufacturing & Supply Company of Avon, Ohio.

Additionally, a method for constructing a non-pneumatic tire inaccordance with the present invention comprises the steps of: sliding acarcass ply structure into engagement with a bladder; seating a firstcircular bead of the carcass ply structure onto a mold; partiallyinflating the bladder to form a bulged carcass ply structure; pouring anelastomer into the mold; seating a second circular bead of the carcassply structure onto a mold cap; closing the mold with the mold cap forenclosing the elastomer; fully inflating the bladder for facilitatingengagement of the elastomer with the carcass ply structure; curing theelastomer; and removing the combined carcass ply structure/elastomerwhich now defines the non-pneumatic tire.

According to another aspect of the present invention, the carcass plystructure comprises a plurality of springs, each spring extending fromthe first circular bead to the second circular bead.

According to still another aspect of the present invention, each springcomprises a first end portion, a second end portion, and an archingmiddle portion interconnecting the first end portion and the second endportion.

According to yet another aspect of the present invention, each spring isinterwoven with an adjacent spring on a first side of the spring andfurther is interwoven with an adjacent spring on a second opposite sideof the spring thereby forming a toroidal carcass ply structure extendingabout an entire circumference of the non-pneumatic tire.

According to still another aspect of the present invention, theelastomer is urethane.

According to yet another aspect of the present invention, the methodfurther includes the step of relocating the self-contained mold/mold capsubsequent to said closing step.

Furthermore, a non-pneumatic tire in accordance with the presentinvention comprises a plurality of springs, which may be helical. Eachspring comprises a first end portion, a second end portion, and anarching middle portion. Each spring is interwoven with at least oneother helical spring thereby forming a toroidal structure extendingabout an entire circumference of the non-pneumatic tire. The toroidalstructure is at least partially coated with an elastomer.

According to still another aspect of the present invention, the springsare secured to an annular rim of a wheel.

According to yet another aspect of the present invention, both the firstand second end portions of each annular spring are secured to theannular rim.

According to still another aspect of the present invention, the toroidalstructure defines a first ply for the non-pneumatic tire.

According to yet another aspect of the present invention, thenon-pneumatic tire is constructed utilizing the method described above.

According to still another aspect of the present invention, thenon-pneumatic tires further comprise a second toroidal structure havingan interwoven toroidal structure with a plurality of springs. The secondtoroidal structure overlaps the first toroidal structure and may have atleast one spring interwoven with at least one spring of the firsttoroidal structure.

According to yet another aspect of the present invention, the secondtoroidal structure is at least partially coated with the elastomer.

Also, a system for constructing a non-pneumatic tire according to thepresent invention comprises a plurality of springs. Each springcomprises a first end portion, a second end portion, and an archingmiddle portion. Each spring is interwoven with at least one other springthereby forming a toroidal carcass ply structure extending about anentire circumference of the non-pneumatic tire. The toroidal carcass plystructure is at least partially coated with an elastomer cured to adhereto the toroidal carcass ply structure.

According to still another aspect of the present invention, the toroidalcarcass ply structure is brought into engagement with a bladder.

According to yet another aspect of the present invention, the toroidalcarcass ply structure further includes two circular beads for seatingthe toroidal carcass ply structure to a mold structure during curing ofthe elastomer.

According to still another aspect of the present invention, theelastomer comprises a two-part polyurethane for chemically curing theelastomer onto the toroidal carcass ply structure at ambienttemperature.

According to yet another aspect of the present invention, the curedelastomer forms a tread portion for generating traction of thenon-pneumatic tire over varied contact surfaces.

According to still another aspect of the present invention, the toroidalcarcass ply structure forms an anisotropic structure having differentmechanical properties in the circumferential direction of thenon-pneumatic tire and the radial direction of the non-pneumatic tire.

According to yet another aspect of the present invention, the systemfurther includes a segmented mold for curing the elastomer to thetoroidal carcass ply structure.

BRIEF DESCRIPTION OF THE DRAWINGS

The structure, operation, and advantages of the present invention willbecome more apparent upon contemplation of the following description asviewed in conjunction with the accompanying drawings, wherein:

FIG. 1 schematically shows a first step of constructing an examplenon-pneumatic tire comprised of a composite material in accordance withthe present invention.

FIG. 2 schematically shows a second step of constructing an examplenon-pneumatic tire comprised of a composite material in accordance withthe present invention.

FIG. 3 schematically shows a third step of constructing an examplenon-pneumatic tire comprised of a composite material in accordance withthe present invention.

FIG. 4 schematically shows a fourth step of constructing an examplenon-pneumatic tire comprised of a composite material in accordance withthe present invention.

FIG. 5 schematically shows a fifth step of constructing an examplenon-pneumatic tire comprised of a composite material in accordance withthe present invention.

FIG. 6 schematically shows a sixth step of constructing an examplenon-pneumatic tire comprised of a composite material in accordance withthe present invention.

FIG. 7 schematically shows a seventh step of constructing an examplenon-pneumatic tire comprised of a composite material in accordance withthe present invention.

FIG. 8 schematically shows an eighth step of constructing an examplenon-pneumatic tire comprised of a composite material in accordance withthe present invention.

FIG. 9 schematically shows a ninth step of constructing an examplenon-pneumatic tire comprised of a composite material in accordance withthe present invention.

FIG. 10 schematically shows a tenth step of constructing an examplenon-pneumatic tire comprised of a composite material in accordance withthe present invention.

FIG. 11 represents a schematic illustration of a conventional wire meshsheet.

FIG. 12 represents a sheet of interwoven helical springs for use withthe composite material of the present invention.

FIG. 13 represents an intermediate step in forming the sheet of FIG. 12.

FIG. 14 represents another intermediate step in forming the sheet ofFIG. 12.

FIG. 15 represents a step in securing two sheets, such as the sheet ofFIG. 12, together.

FIG. 16 represents an example helical spring for use with the compositematerial of the present invention.

FIG. 17 represents the helical spring of FIG. 16 in a deflectedcondition.

FIG. 18 represents a schematic illustration of an example tire and wheelassembly comprised of the composite material of the present invention.

FIG. 19 represents a section taken through line 19-19 in FIG. 18.

FIG. 20 represents a section taken through line 20-20 in FIG. 19.

FIG. 21 represents a schematic perspective view of an example tire of acomposite material of the present invention.

FIG. 22 represents a schematic orthogonal view of the tire of FIG. 21.

FIG. 23 represents a schematic cross-sectional view of the tire of FIG.21.

FIG. 24 represents a schematic of an example load/deflection curve.

FIG. 25 represents a schematic of another example load/deflection.

FIG. 26 represents a schematic of still another example load/deflectioncurve.

FIG. 27 represents a schematic of yet another example load/deflectioncurve.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS OF THE COMPOSITE MATERIAL OFTHE PRESENT INVENTION

A system may comprise a method 500 of constructing a tire fornon-pneumatic support of a vehicle, a non-pneumatic tire 100 forsupporting a vehicle, or both.

The method 500 may include providing a segmented cylindrical open-endedmold 510, a circular mold cap 520 corresponding to the mold, and aninflatable/expandable bladder 530. In a first construction step 501, anopen ended cylindrical carcass ply, for example the carcass ply definedby the springs 310 below, may be slid over, or lowered around, thebladder 530. In a second step 502, a first circular bead 541 is seatedin a corresponding first circular groove (not shown) in the mold 510. Ina third step 503, the bladder 530 is partially inflated to form a bulgedply. In a fourth step 504, an elastomer 550, such as polyurethane, ispoured into the mold 510. In a fifth step 505, the mold cap 520 islowered into closing engagement with the mold 510 thereby seating asecond circular bead 542 in a corresponding second circular groove (notshown) in the mold cap and also axially compressing the beads 541, 542of the carcass ply creating a toroidal carcass structure. In a sixthstep 506, the bladder 530 is further inflated, thereby expanding thecarcass ply further and facilitating flow of the elastomer 550 aroundthe exposed surfaces of the carcass ply. Air and excess elastomer 550may be expelled from the interior of the mold/mold cap 510, 520 througha one-way check valve (not shown) in the mold/mold cap during this sixthstep 506.

In a seventh step 507, the bladder 530 is fully inflated, thereby fullyexpelling air and excess elastomer 550 from the interior of themold/mold cap 510, 520. Following this seventh step 507, the mold/moldcap assembly 510, 520 may be relocated to a convenient location sincethe assembly is self-contained at this point. In an eighth step 508,following a sufficient cure time, the bladder 530 is deflated, the moldcap 520 is raised out of engagement with the mold 510, and the moldsegments 511 are disengaged from each other and the newly cured tire600. In a ninth step 509, the tire 600 is fully removed from engagementwith the bladder 530 and is ready for use.

During the fifth, sixth, and seventh steps 505-507, the actualdimensions of the bladder 530, mold/mold cap 510, 520, and carcass plywill determine whether the carcass ply will be completely encased by theelastomer 550 (FIG. 23) or the inner surface of the carcass ply formsthe inner toroidal surface of the tire 600. In other words, the fullyinflated bladder 530 will either directly engage the inner surface ofthe carcass ply, expanded by the axial converging of the beads 541, 542,thereby forming a tire 600 having an inner toroidal surface which is theinner surface of the carcass ply; or the fully inflated bladder will notreach the inner surface of the carcass ply, thereby allowing theelastomer to flow into that gap and forming a completely encased carcassply.

An example tire 300, 600 may include an interwoven, or interlaced,plurality of helical springs (i.e., coiled wires which deformelastically under load with little energy loss). The tire 300, 600 maydefine a toroidal shaped structure for mounting to a wheel 200. The tire300, 600 may contour to a surface on which the tire engages tofacilitate traction while mitigating vibration transmission to acorresponding vehicle. The helical springs support and/or distribute aload of the vehicle. The tire 300, 600 may be pneumatic ornon-pneumatic.

Under the weight of a vehicle, the tire 300, 600 may be driven, towed,or provide steering to the vehicle. The helical springs of the tire 300,600 may passively contour to any terrain by flexing and moving withrespect to each other. The interwoven structure of the helical springsprovides stability to the tire 300, 600 and prevents the structure fromcollapsing as the tire rotates and engages variable terrain.

The helical springs of the tire 300, 600 may be resilient through afinite range of deformation, and thus a relatively rigid frame similarto a carcass ply may be used to prevent excessive deformation. Radiallyoriented portions of the springs may be used to connect the tire 300,600 to the wheel 200. These springs may be interwoven, or interlaced.Other springs may be incorporated with the tire at any bias angle, fromradial to circumferential, with the purpose of distributing load. Theseother springs may be helical springs. Further, as one example, theseother springs may extend circumferentially around the tire at a radiallyouter portion of the tire 300, 600.

External covering of some kind (i.e., a tread, an elastomer 550) may beadded to partially or fully protect the helical springs from impactdamage and/or to change the tire's ability to float and generatetraction. As one example, four basic steps may be utilized tomanufacture one example carcass ply structure for the tire 300, 600: i)twisting helical springs together to form a rectangular sheet with alength corresponding to the desired tire circumference; ii) interweavingends of the rectangular sheet of springs to form a mesh cylinder (FIG.2); iii) collapsing one end of the mesh cylinder and attaching it to arim of a wheel 200; and iv) flipping the other end of the mesh cylinderinside out and attaching it to another axially opposite rim of the wheel200.

The example tire 300, 600 may be utilized on Earth, the Moon, Mars,and/or any other planetary body, since its elements operate reliably inatmospheric and terrain conditions of these planets. The tire 300, 600may be utilized on its own, or incorporated as a partial or auxiliaryload support/distribution system within another tire type. The tire 300,600, however, requires no air, operates in difficult environments, andcontours to all terrains.

The tire 300, 600 provides an improvement over the conventional wiremesh, non-pneumatic tire of the Apollo LRV. The tire 300, 600 provideshigher load capacity, since wire size of the helical springs may beincreased with relatively little functional alteration. The tire 300,600 provides a longer cycle life, since wire stresses of the helicalsprings are more uniformly distributed throughout the carcass ply-likestructure. Further, the tire 300, 600 provides relatively low weight perunit of vehicle weight supported, since the interwoven helical springnetwork (like a carcass ply) is fundamentally stronger than the crimpedwire mesh. Additionally, helical springs are able to compress andelongate to accommodate manufacturing variations. Finally, the tire 300,600 provides improved design versatility, since load distributionsprings may be added to vary the tire strength in different tirelocations and directions.

The example tire 300, 600 may further provide relatively low energy losscompared to tires that use frictional or hysteretic materials in acarcass, since the helical springs consume near zero energy duringdeformation. The example tire 300, 600 contains redundant load carryingelements and may operate normally even after significant damage. Theexample tire 300, 600 may thus be utilized for low vehicle energyconsumption, for tire failure posing a critical threat, for travelingthrough rough terrain, for exposure to extreme temperatures or highlevels of radiation, and/or for exposure to gun fire or bomb blasts.

As shown in FIG. 11, a woven wire mesh has been used for a conventionallunar tire. However, as discussed above, greater strength and durabilityis desired. FIG. 12 shows a mesh sheet 50 of interwoven helical springs55 that may provide greater strength and durability than the wire mesh.FIGS. 13, 14, and 15 show intermediate steps in forming a mesh sheet 50as shown in FIG. 12. In FIG. 13, a first helical spring 55 is shownbeing rotated thereby interweaving that same first spring with a secondhelical spring 55. In FIG. 14, a third helical spring 55 is shown beingrotated thereby interweaving that third spring with the already wovenfirst and second springs 55. In FIG. 15, a helical spring 55 is shownbeing rotated for connecting two mesh sheets 50 (i.e., the sheet of FIG.12) of helical springs 55. FIG. 6 shows a single helical spring 55 foruse as described above in FIGS. 12-15. FIG. 17 shows a single helicalspring 55 deflected for use in a tire such as the tires 300, 600, asdescribed below.

As shown in FIGS. 18-20, an example assembly 100 includes a wheel 200and a tire 300. The wheel 200 has an annular rim 202 at each axial sidefor securing the tire 300 to the wheel. Each rim 202 is fixed relativeto the other rim 202. Each rim 202 may include a plurality of socketholes 204 for aligning the tire 300 with the rim. Any other suitablemeans may be used for securing the tire 300 to the rim 200.

The example tire 300 may include a plurality of helical springs 310extending radially away from the wheel 200 in an arching configurationand radially back toward the wheel. Each end 315 of each spring 310 maybe secured to wheel at a corresponding rim 202 of the wheel. Each spring310 has a middle portion interconnecting the ends 315. Each end 315 maybe secured at an axial orientation (FIG. 19) or at an angledorientation, with each spring 310 extending axially outward from one rim202, then away from the wheel 300, then back over itself, then inward,and finally axially toward the other rim 202. Each end 315 of eachspring may thereby be oriented coaxially (or at an angle) with the otherend 315 of the same spring.

Further, each spring 55 may be interwoven with adjacent springs 55 (FIG.12) enabling load sharing between springs. As shown in FIG. 12, eachspring 55 is interwoven, or interlaced, with an adjacent spring 55 on afirst side of the spring and further being interwoven with an adjacentspring 55 on a second opposite side of the spring. Thus, the springs 310extend radially and axially and form a woven toroidal structure, similarto the carcass ply of a pneumatic tire, extending about an entirecircumference of the tire 300 (FIGS. 8-10).

The helical springs 310 may be any suitable length, gauge, pitch, andshape (i.e., oval springs, elliptical springs, etc.). The helicalsprings 310 may vary in coil diameter (i.e., barrel springs may be used)to create continuity in the mesh through the range of radial positionsin the tire 300 (i.e., narrower coil width at the beads). The helicalsprings 310 may be further structured as two or more plies, one or moreradially inner plies being radially overlapped by one or more radiallyouter plies. Further, at least one helical spring of one ply may beinterwoven with at least one helical spring of another ply foradvantageously increasing strength of the overall structure. The helicalsprings 310 may be Ti—N alloy, steel, titanium, polymer, ceramic, or anyother suitable material.

The purely metallic, non-pneumatic spring tire 300 described above hasbeen developed for space applications. The structure is a series ofinterwoven springs as seen in FIG. 20. This structure was well suited tospace applications where rubber is not permitted due to temperaturevariations (40K to 400K). In addition, the spring tire 300 may achieveexcellent traction where soil composition may be soft sand such as theMoon.

On Earth, however, the variety of road surfaces causes the purelymetallic contact interface of the above example tire 300 to have limitedapplication. Based on this limited commercial application, theinterwoven structure of the example tire 300 may be enhanced forterrestrial applications.

In order to achieve traction on the wide variety of terrestrial roadsurfaces, a polymer may be added to the all-metal example tire 300 toserve as a tread. For step 504 of the method 500, one option is to use atwo-part polyurethane that may be poured into the mold 510 containingthe pre-assembled example spring tire 300. Once the two parts are mixedtogether, a chemical reaction occurs that cures the polymer at ambienttemperature and pressure. Once the cure is complete, the resulting tire300 is removed from the form and is ready for use.

In laboratory samples, fatigue was tested per the dimensions from Table1 below with cycling of over one million cycles with a deflection of 1.5inches. Based on prospective load requirements and terrainspecifications, a polymer coated tire was exemplarily targeted at anall-terrain vehicle (ATV). As shown in FIGS. 21-23, such an example tire600 was determined to have load/deflection characteristics indicated bythe load/deflection curve of the non-pneumatic tire 600 shown in FIG.24. The structural stiffness of the tire 600 was significantly higherthan was expected from the spring structure itself. The polymer used,urethane, itself not only carries some load in bending, but alsoconstrains the spring motion in such a way (e.g. prevention of rotation)as to increase the bending stiffness of the springs.

Outer Diameter (mm) 6.985 Inner Diameter (mm) 4.318 Wire FilamentDiameter (mm) 1.397 Spring Pitch (mm) 6.620

As shown in FIGS. 21-23, the rims 202 used for the example lunar springtire 300 may not be utilized with the method 500. A rim similar to thoseused for standard pneumatic tires may be used with the method 500 toproduce the example tire 600. By way of example only, three optionsare: 1) a custom rim designed specifically for the particular vehicleand service application; 2) a standard (commercially available) rim, forlight duty applications; and 3) a standard (commercially available) rimmodified to allow mechanical fasteners to fix the tire bead to the rim(since the beads 541, 542 need not have an air-tight engagement with therim).

The example polymer/spring tire 600 thus partially shares its loadcarrying mechanism with lunar spring tire 300 (i.e., the interwovenspring carcass-like structure). Additionally, the polymer encasedinterwoven spring ply becomes an anisotropic ply, with differentproperties along the axes and transverse to the spring axes. However,unlike typical fiber reinforced plies, the reinforcing springs 310themselves have a bending stiffness, due to the width of the helixes ofeach spring, which may be greater than bending stiffness of thereinforcing filaments or yarns alone.

This additional bending stiffness contributes significantly to theoverall bending stiffness of the interwoven spring ply. Since bendingstiffness carries the load placed on the example spring ply tires 300,600, this is contrary to conventional pneumatic tires, which carry loadin tension away from the footprint in the cords (filaments or yarns) ofthe upper segment of the pneumatic tire. Other conventionalnon-pneumatic tires also carry loads by tension in members in an uppersection of such tires. Thus, an interwoven spring tire of aspring/polymer composite in accordance with the present invention mayproduce a bottom-loaded structure unlike conventional tires. As shown inFIGS. 21-23, the polymer coating of the interwoven spring ply may form atread pattern 601 designed for traction with the spring ply structurecarrying part of the load.

The example polymer 550 may comprise an elastomeric material which mayhave a Young's modulus E from about 21 Kg/cm² to about 21,000 Kg/cm².The tensile modulus at 300% may be 161 Kg/cm² or 915.9 MPa. As anotheralternative, a Young's modulus greater than 140 Kg/cm² may require amixture of polyurethane and chopped fibers of an aromatic polyamide.Also, boron may be mixed with polyurethane.

As stated above, a carcass ply structure 300 of radial springs 310produces excellent load bearing performance in the example non-pneumatictire 300 or 600. This carcass ply structure 300 thus enhances theperformance of the example non-pneumatic tire 300 or 600. Thoughnon-pneumatic, the similarity of the carcass ply structure 300 to atraditional pneumatic tire carcass ply produces an instructivecomparison.

The complexities of the structure and behavior of the pneumatic tire aresuch that no complete and satisfactory theory has been propounded.Temple, Mechanics of Pneumatic Tires (2005). While the fundamentals ofclassical composite theory are easily seen in pneumatic tire mechanics,the additional complexity introduced by the many structural componentsof pneumatic tires (and the example non-pneumatic tire 300, 600) readilycomplicates the problem of predicting tire performance. Mayni, CompositeEffects on Tire Mechanics (2005). Additionally, because of thenon-linear time, frequency, and temperature behaviors of polymers andrubber (and elastomers), analytical design of pneumatic tires is one ofthe most challenging and underappreciated engineering challenges intoday's industry. Mayni.

A pneumatic tire (and the example non-pneumatic tire 300, 600) hascertain essential structural elements. United States Department ofTransportation, Mechanics of Pneumatic Tires, pages 207-208 (1981). Animportant structural element is the carcass ply, typically made up ofmany flexible, high modulus cords of natural textile, synthetic polymer,glass fiber, or fine hard drawn steel embedded in, and bonded to, amatrix of low modulus polymeric material, usually natural or syntheticrubber. Id. at 207 through 208. The example non-pneumatic tire 300, 600in accordance with the present invention has a carcass ply structure 300of radial springs 310.

The flexible, high modulus cords are usually disposed as a single layer.Id. at 208. Tire manufacturers throughout the industry cannot agree orpredict the effect of different twists of carcass ply cords on noisecharacteristics, handling, durability, comfort, etc. in pneumatic tires,Mechanics of Pneumatic Tires, pages 80 through 85. A prediction of theeffect of interweaving helical springs on noise characteristics,handling, durability, comfort, etc. is even less likely.

These complexities are demonstrated by the below table of theinterrelationships between tire performance and tire components.

LINER CARCASS PLY APEX BELT OV'LY TREAD MOLD TREADWEAR X X X NOISE X X XX X X HANDLING X X X X X X TRACTION X X DURABILITY X X X X X X X ROLLRESIST X X X X X RIDE COMFORT X X X X HIGH SPEED X X X X X X AIRRETENTION X MASS X X X X X X X

As seen in the table, carcass ply cord characteristics affect the othercomponents of a pneumatic tire (i.e., carcass ply affects apex, belt,overlay, etc.), leading to a number of components interrelating andinteracting in such a way as to affect a group of functional properties(noise, handling, durability, comfort, high speed, and mass), resultingin a completely unpredictable and complex composite. Thus, changing evenone component can lead to directly improving or degrading as many as theabove ten functional characteristics, as well as altering theinteraction between that one component and as many as six otherstructural components. Each of those six interactions may therebyindirectly improve or degrade those ten functional characteristics.Whether each of these functional characteristics is improved, degraded,or unaffected in the example non-pneumatic tire 300, 600, and by whatamount, certainly would have been unpredictable without theexperimentation and testing conducted by the inventors.

Thus, for example, when the structure (i.e., spring stiffness, springdiameter, spring material, etc.) of the carcass ply structure 300 of theexample non-pneumatic tire 300, 600 is modified with the intent toimprove one functional property of the non-pneumatic tire, any number ofother functional properties may be unacceptably degraded. Furthermore,the interaction between the carcass ply structure 300 and the curedelastomer 550 may also unacceptably affect the functional properties ofthe non-pneumatic tire. A modification of the carcass ply structure 300may not even improve that one functional property because of thesecomplex interrelationships.

Thus, as stated above, the complexity of the interrelationships of themultiple components makes the actual result of modification of a carcassply structure of a non-pneumatic tire, in accordance with the system ofthe present invention, impossible to predict or foresee from theinfinite possible results. Only through extensive experimentation havethe carcass ply structure 300 and elastomer 550 of the system of thepresent invention been revealed as an excellent, unexpected, andunpredictable option for a non-pneumatic tire.

As partially described above, a composite material in accordance withthe present invention may comprise a series of interwoven springsembedded in a polymer. The mechanical properties of such a compositematerial produce more than the mere superposition, or addition, of thestrengths of the springs and the polymer (not a mere-collocation oraggregation).

Further, properties of the composite material may be easily tunable.Bending stiffness may be tuned by changes to the material, pitch,filament diameter, and diameter of the springs. Weight may be tuned bychanges to the spring and/or polymer material. Damping and viscouslosses may also be tuned by changes to the spring and/or polymermaterial.

The springs of the composite material may be in the shape of an ellipseor other helix to conform to spatial restraints. Further, the springsmay be of diverse materials, such as metal, plastic, polyurethane,rubber, and carbon (as described above). The springs need not be coatedor treated to create adhesion with the polymer matrix, as mechanicalinterlocking of the springs with the cured polymer provides anappropriate securement mechanism.

The “free-density” of springs may be (a) tightly laterally compressed or(b) tightly laterally tensioned. Thus, for case (a), each spring islaterally compressed with an adjacent spring such that an outer part ofeach coil of each spring engages an inner part of each coil of theadjacent spring. For case (b), each spring is laterally tensioned withan adjacent spring such that an inner part of each coil of each springengages an inner part of each coil of the adjacent spring.

In case (a), the distance between one spring and its neighbor isapproximately the spring filament diameter. In case (b), the distance isapproximately the coil diameter minus the filament diameter. Forexample, the above example tires 300, 600 have laterally compressedsprings (case (a)) in the bead area for a high stiffness transitioningto laterally tensioned springs (case (b)) in the crown to produce lowstiffness needed for obstacle enveloping and for eliminating tire outerdiameter growth with speed or load (FIG. 20).

For example, the measured vertical stiffness of an example ATV tire 600was 1590 lb/in. In contrast, an example lunar tire 300, havingapproximately 30% more springs configured in a beam spring arrangement,had a stiffness of 589 lb/in. The 270% higher vertical stiffness of theexample tire 600 with the springs embedded in polymer cannot beattributed to the addition of the polymer alone, but to the combinationof the springs and polymer—a mesh locking effect.

Another example spring may be constructed of Normal Tensile (NT) steel,clean and uncoated with a 0.35″ spring OD, 0.055″ wire diameter, 0.28″pitch, and with the springs placed in lateral tension. The polymer maybe high durometer (80-90) urethane, such as “Repro 83” from ReproUrethanes, Poly PT Flex 20, Poly PT Flex 60, Poly PT Flex 70, Poly PTFlex 80, and/or Poly PT Flex 85 from Polytek Development Corporation ofEaston, Pa., and/or a castable elastomer such as Fast-Cast Urethane fromFreeman Manufacturing & Supply Company of Avon, Ohio. The compositematerial in accordance with the present invention may be exemplarilyused as a non-pneumatic tire material or a runflat structure materialsuch as an insert in a pneumatic tire. The composite material may alsoimprove the puncture resistance and/or the structural stiffness of anystructure.

Conventional composite materials usually rely on the embedding ofreinforcing fibers or cords in an elastomer matrix. The fibers/cords aretypically cylindrical, with a length (l) and a diameter (d). Suchfibers/cords may be long (l>>d) or short (l>d), but usually have a hightensile stiffness with respect to the polymer matrix. The bendingstiffness of such fibers/cords, however, is typically low because of lowarea moment of inertia (I=Pi*d^4/64) and small diameter of thefiber/cord. Conventional materials, however, may achieve high bendingstiffness as the fibers/cords are loaded in tension and compression asthe material is bent by an amount dependent on the position of thefibers/cords relative to the neutral axis of bending.

In comparison to the conventional material, the composite material ofthe present invention derives bending stiffness from the bendingstiffness of the spring mesh itself, the bending stiffness of thepolymer, and the mechanical restriction of relative motion between thesprings and the other springs and the polymer (mesh locking effect). Themesh locking effect may thus cause the bending stiffness of thecomposite material to be greater than the bending stiffness of thespring mesh added to the bending stiffness of the polymer (i.e., 9%greater in the example graph of a spring/rubber composite in FIG. 25).Thus, the spring mesh and polymer are more than a mere collocation oraggregation of strengths.

Also, adhesive bonding between a reinforcing material and an elastomeris critical, because there is little or no physical interlocking betweenthe fibers/cords and elastomer. Thus, if standard fibers/cords “de-bond”from the elastomer, mechanisms like socketing may occur where thefiber/cord loses all contribution to the composite material's mechanicalstrength (i.e., bending stiffness). In a composite material inaccordance with the present invention, mechanical interlocking is asignificant mechanism securing the reinforcing springs in the polymerand contributing to the composite material's structural properties.

The example graph of FIG. 26 illustrates an increase of 20.1% over themere addition of stiffness of the springs and the polymer Poly PT Flex60.

The example graph of FIG. 27 illustrates an increase of 32.5% over themere addition of stiffness of the springs and the polymer Poly PT Flex70

In the foregoing description, certain terms have been used for brevity,clearness, and understanding; but no unnecessary limitations are to beimplied therefrom beyond the requirement of the prior art, because suchterms are used for descriptive purposes and are intended to be broadlyconstrued. Moreover, the description and illustration of the presentinvention is by way of example, and the scope of the present inventionis not limited to the exact details shown or described.

Having now described the features, discoveries, and principles of thepresent invention, the manner in which the present invention isconstructed and used, the characteristics of the construction, and theadvantageous, new, and useful results obtained, the scope of the new anduseful structures, devices, elements, arrangements, parts, andcombinations are hereby set forth in the appended claims.

What is claimed:
 1. A composite material comprising a plurality ofsprings forming a structure embedded within polyurethane, each springbeing interwoven with at least one other spring thereby forming anentirely polyurethane-coated structure, the composite material forming atoroidal carcass structure extending about an entire circumference of anon-pneumatic tire, each spring including a first end portion, a secondend portion, and an arching middle portion interconnecting the first endportion and the second end portion, each first end portion being securedto a first annular bead and each second portion being secured to asecond annular bead, the first and second annular beads both beingseated to a wheel rim such that the toroidal carcass structure issecured to the wheel rim wherein the springs are elliptical.